Quantcast. It's a great site for getting something one-off noticed. For instance, although I write mostly about business and Egypt, I have a seasonal Squidoo lens about gingerbread houses which is getting 800 unique visitors a week. Not massive in FTSE / NASDAQ terms, but for an owner-managed-business that's worthwhile. For any author, it's flattering to have that sort of readership. If you are interested in seeing more, these are my top Squidoo pages, or join Squidoo. I just wish my lens about twilight birthday cakes and parties would do better - more about that later!
The alternative is HubPages. Newer than Squidoo, it's ranked #93 with 9.2m American visitors each month. I've been less active on HubPages than Squidoo and my most successful hub (great sax solos) has less traffic in total than my top Squidoo lens is getting in a week. Both sites are supported by adverts but HubPages has a generally lower ad-burden than Squidoo so may seem more attractive to business. However, on Squidoo it's possible to turn adverts off. As a marketeer, I don't do that often (although I do set some lenses to be charitable, donating all of my income to charity), but my lens about my father's art (PT Phiz) has all of the adverts removed. That's a format which would suit a business. Hubpages also limits outbound links to 2 per domain; Squidoo's limit of 9 is more reasonable. For those reasons, I think Squidoo suits buisiness and professionals better than Squidoo.
The key, in both cases is promition - SEO if that's the term you prefer to use. That's the issue with my Twilight birthday lens - Google doesn't like it. Some topics need little promotion, but if you wanted to promote a product it may need some work. It could suit an artist, though, who wants a suit to describe her work but doesn't want the overhead of a dedicated web site. Of course, any Squidoo lenses of Hubpages hubs you create will have an SEO advantage on your other sites if you link them from the lens / hub
Neither Squidoo nor HubPages is perfect. Neither is an answer to all problems. But they can have a role to play.